Summons one of your hero's boats to their current location. If none of those boats are available, then one of your other heroes' boats is summoned. Spell has a 50% chance of working. The spell fails if there are no unoccupied boats available.

Advanced effect

Same as basic effect, except that if no boats are available, a new one is created. The spell has a 75% chance of working. There are a maximum of sixty-four boats allowed on the Adventure Map at one time. The spell fails if all are occupied.

Expert effect

Same as advanced effect, except that the spell has a 100% chance of working (unless all sixty-four boats are occupied).

The spell may only be cast on the Adventure Map and next to a shoreline. In order to Summon Boat spell to work, there must be an unoccupied (free) tile to summon the boat. Additionally, on basic level there must also be an unoccupied boat somewhere on the map. At advanced and expert level, a boat will be created if there are no free boats to summon. Summoning a boat will make the closest unoccupied boat to disappear, which sometimes can lead to tactical choice to cast the spell.

It is referred in the description of expert level Summon Boat spell, that the spell could fail if all possible 64 boats are occupied. However, boats cannot be summoned if a hero is already in a boat, and there can only be 64 heroes wandering on the Adventure Map at the same time. This leads to a situation, that if all heroes are in the boats, none of them can cast the spell.